UNIVERSITY  OF  CALIFORNIA 

AGRICULTURAL  EXPERIMENT  STATION 

E.   W.    HILGARD,    DIRECTOR 


ORCHARD    FUMIGATION 


C.  W.  WOODWORTH 
Entomologist 


The  Cottony  Cushion  Scale 
against  which  fumigation  was  first  practiced 


BULLETIN   122 


BERKELEY 

Zbe  THntvevsit£  {press 

January,   1899 


ORCHARD  FUMIGATION.* 


By  C.  W.  Woodworth. 


The  fumigation  of  orchards  has  never  been  practiced  in  California 
outside  of  the  seven  southern  counties,  and  there  only  in  the  citrus 
belt.  It  has  supplanted  spraying  almost  entirely  in  much  of  this 
region,  however,  and  there  seems  to  be  no  reason  why  it  should  not 
be  found  equally  satisfactory  in  other  parts  of  the  State. 

Though  much  has  been  written  on  this  subject  there  is  nothing  that 
gives  a  comprehensive  account  of  the  methods  now  in  use.  This 
bulletin  has  been  prepared  to  supply  this  information  and  to  awaken, 
a  wider  interest  in  the  matter  of  fumigation.  The  experience  with 
fumigation  in  the  East  emphasizes  its  value  as  a  means  of  utterly 
destroying  newly  introduced  scale  insects;  and  there  is  greater  reason 
for  hope  to  entirely  eradicate  such  insects  with  this  process  than  by 
any  other  known  method  except  the  destruction  of  the  infested  trees. 

Without  any  question,  the  most  thoroughly  effective  of  all  the 
insecticides  which  have  been  applied  to  plants  is  hydrocyanic  acid 
gas.  The  discovery  of  its  value  and  the  development  of  the  method 
of  its  application  forms  one  of  the  most  interesting  chapters  in 
economic  entomology.  But  for  the  ravages  of  the  cottony  cushion 
scale  the  process  might  never  have  been  discovered,  and  had  not  the 
red  scale  become  very  destructive  it  might  have  been  cast  aside  as 
impractical;  it  required  the  invasion  of  San  Jose  scale  to  carry  the 
method  into  the  Eastern  States. 

Historical. 

As  introductory  to  the  review  of  our  present  methods  it  will  be 
advantageous  to  outline  briefly  the  history  of  their  discovery  and 
development.  The  cottony  cushion  scale  which  was  introduced  into 
California  from  Australia,  many  years  ago,  gradually  spread  over  the 
State,  reaching  Southern  California  about  twenty  years  ago;  and  after 
a  few  years  had  so  increased  as  to  threaten  the  very  existence  of  the 
citrus  orchards  in  that  region.  Almost  driven  to  despair,  the  growers 
made  a  very  urgent  appeal  to  the  United  States  Entomologist,  Professor 
Riley,  who  detailed  two  assistants  to  undertake  the  study  of  the 
methods  of  controlling  the  insect.  One  of  these  was  Mr.  D.  W. 
Coquillett,  whose  name  will  always  be  associated  with  orchard  fumiga- 
tion as  the  first  discoverer  of  the  value  of  h3Tdrocyanic  acid  gas  for 
this  purpose. 

*A  resume  of  this  bulletin  will  be  found  on  page  33.  Most  of  the  figures  are  from  photographs 
taken  for  this  bulletin  by  Mr.  J.  W.  Mills  of  the  Station  at  Pomona.  Fig.  12  is  from  the  Report  of 
the  State  Board  of  Horticulture,  and  Fig.  13  from  Bulletin  57  of  the  Maryland  Agricultural  Experiment 
Station. 


The  Department  of  Agriculture  had  no  part  in  the  discovery  of 
the  value  of  this  method,  for  after  employing  Mr.  Coquillett  for  some 
six  months,  during  which  time  he  experimented  with  various  sprays, 
he  was  "laid  off"  owing  to  an  insufficient  appropriation.  Mr.  Coquillett 
continued  to  work  on  the  problem  of  destroying  the  scale,  though  at 
his  own  expense,  and  finally  in  September,  1886,  he  began  seriously  to 
study  the  methods  of  fumigation.  These  had  been  inaugurated  by 
various  parties,  prominent  among  whom  were  Mr.  J.  W.  Wolfskill  and 
his  very  able  foreman  Mr.  Alexander  Craw.  At  their  place  Mr. 
Coquillett  began  his  experiments,  profiting  by  the  work  already  done 
by  these  gentlemen  and  by  the  facilities  here  provided,  and  here  he 
first  conceived  the  idea  of  using  hydrocyanic  acid  gas.  Some  six 
months  were  devoted  to  the  perfecting  of  the  method,  which  they 
hoped  to  patent  and  profit  by,  and  it  was  therefore  guarded  as  a 
profound  secret. 

Mr.  Coquillett  did  not  give  to  the  world  the  knowledge  of  the  value 
of  hydrocyanic  acid  gas,  but  it  came  from  another  discovery  which 
resulted  through  the  public  spirit  of  certain  growers.  The  success  of 
fumigation  at  the  Wolfskill  place  became  widely  known,  and  those  who 
.were  seeing  their  trees  die  from  the  effect  of  the  scale  were  naturally 
impatient  to  know  a  remedy.  Finally,  a  number  of  growers  about 
San  Gabriel  appealed  to  Professor  Hilgard  and  asked  for  a  chemist  to 
experiment  with  gases  to  find  out  what  would  best  effect  the  results 
desired.  Mr.  F.  W.  Morse  was  delegated  for  this  work  and  found, 
like  Mr.  Coquillett,  that  hydrocyanic  acid  gas  was  by  far  the  most 
satisfactory.  In  the  course  of  these  experiments  certain  parties 
who  had  witnessed  some  of  the  former  experiments,  recognized  the 
odor  of  the  gas,  and  thus  the  secret  that  was  so  jealously  guarded 
became  known  to  the  public.  The  honor  of  making  known  the  value 
of  this  insecticide  thus  lies  with  Mr.  Morse  and  Professor  Hilgard, 
under  whose  directions  the  experiments  were  made. 

The  experiments  conducted  by  Mr.  Morse  were  reported  by  him  in 
Bulletin  71  of  this  Station,  and  thus  vanished  for  Mr.  Coquillett  both 
the  honor  and  hope  of  profit  from  the  discovery  made  six  months  before. 
Mr.  Coquillett,  however,  continued  to  experiment,  becoming  again  an 
assistant  in  the  Department  of  Agriculture,  and  did  more  than  any 
other  person  to  develop  and  perfect  our  present  methods  of  fumigation. 

Injury  to  Foliage'. — The  problem  of  fundamental  importance  in 
fumigation  is  that  of  preventing  injury  to  the  plant.  It  is  not  a  hard 
matter  to  kill  an  insect  with  almost  any  chemical,  if  used  strong 
enough;  but  to  do  this,  without  also  at  the  same  time  injuring  the  tree, 
is  often  a  difficulty  that  cannot  be  overcome.  This  difficulty  has  been 
the  chief  one  to  contend  against  in  perfecting  the  method  of  fumiga- 
ting with  this  gas. 

The  first  method  by  which  the  reduction  of  injury  was  accomplished 
was  the  soda  process  of  Morse,  which  consisted  in  adding  ordinary 
baking  soda  to  the  cyanide  solution,  using  something  like  two  and  a 
half  times  as  much  soda  as  there  is  cyanide  in  the  solution,  the  result 
being  the  production  of  carbonic  acid  gas,  thus  diluting  the  hydrocyanic 
acid  gas. 

Previous    to    the    time    of    the    publication    of    this    method    Mr. 


Coquillett  accomplished  a  similar  diminution  of  the  injury,  by  the 
slow  generation  of  the  acid,  which  he  accomplished  by  means  of  a 
generator  consisting  of  two  parts,  from  one  of  which  the  sulphuric 
acid  passed  in  a  fine  stream,  regulated  by  a  stopcock,  into  the  other 
containing  dry  cyanide.  This  was  made  known  through  a  paper,  by 
Mr.  Alexander  Craw,  read  before  a  meeting  of  fruit  growers  held  at 
Los  Angeles  in  October,  1887. 

A  third  plan  was  soon  devised  by  Mr.  Coquillett,  called  by  him  the 
"dry  gas  process,"  which  consisted  in  passing  the  gas  from  the 
generator  through  sulphuric  acid  before  allowing  it  to  come  in  contact 
with  the  foliage.  In  this  he  followed  Morse's  idea  of  using  a  solution 
of  cyanide.  This  was  the  situation  at  the  time  of  the  publication  of 
Mr.  Coquillett' s  first  paper,  wherein  these  three  processes  were  de- 
scribed quite  fully,  as  here  outlined.  He  strongly  recommended  his 
last  process  as  the  cheapest  and  most  convenient;  and  Mr.  Morse,  in  a 
later  paper,  practically  abandoned  his  soda  method  in  favor  of  the  dry 
gas  process. 

The  reasons  for  the  injury  have  been,  from  the  first,  matters  for 
speculation  and  controversy,  and  even  to-day  it  must  be  confessed  that 
we  are  far  from  possessing  sufficient  data  to  enable  us  to  solve  any 
considerable  part  of  the  problem.  From  the  first  the  results  have 
been  very  uncertain,  proving  that  there  are  a  number  of  factors 
involved.  One  of  the  earliest  to  be  suggested  was  that  faulty  dis- 
tribution of  the  gas  would  tend  to  cause  burning  wherever  the  pure 
or  slightly  diluted  gas  came  in  contact  with  the  leaves.  The  experi- 
ence in  the  field  bore  out  this  idea,  so  that  in  most  of  the  earlier  work 
elaborate  provision  was  made  for  the  mixing  of  the  gas  and  the  air 
contained  in  the  tent.  These  provisions  were  generally  some  form  of 
blower  connected  with  the  generator.  Later  work  has  demonstrated 
that  this  is  of  minor  importance. 

Mr.  Coquillett7 s  first  theory  was  that  the  mixing  or  perhaps  the 
combination  of  the  gas  with  water  rendered  it  more  injurious,  and 
both  of  his  processes  were  based  on  this  idea;  he  explained  the 
effectiveness  of  the  soda  process  as  arising  from  the  affinity  of  the 
carbonic  acid  for  water. 

Mr.  Morse's  original  ideas  are  not  made  plain  in  his  writings,  but 
his  later  studies  led  him  to  believe  that  the  development  of  ammonia  in 
the  gas  was  the  most  important  cause  of  injury.  The  injurious  effects  of 
ammonia  are  well  known,  and  he  demonstrated  the  presence  of  ammonia 
in  the  gas,  especially  in  that  generated  from  a  solution  of  cyanide. 
Thus  we  have  two  theories  accounting  for  the  good  effects  of  the 
methods  then  known,  and  both  agreed  in  favoring  the  dry  gas  process. 
The  latter  theory  seems  to  have  had  more  foundation  in  fact,  but  it 
soon  became  evident  that  there  were  other  still  more  important  factors 
determining  the  injury  to  the  foliage. 

The  results,  as  regards  the  injury  to  the  trees,  continued  to  be 
unreliable  to  a  certain  degree,  and  this  fact,  coupled  with  the  wonder- 
fully promising  results  of  the  importation  of  ladybirds  from  Australia, 
caused  the  method  to  be  laid  aside  to  a  good  extent. 

Fumigation  for  Red  Scale. — The  revival  of  the  interest  in  fumigation 
arose  from  the  fact  that  the  red  scale  soon  became  very  troublesome  in 


Orange  County.  Mr.  Coquillett  was  invited  to  conduct  experiments 
in  the  orchard  of  Mr.  A.  D.  Bishop  with  his  apparatus,  and  here  great 
steps  were  made  towards  the  perfection  of  the  method. 

The  Most  Destructive  Scale  Insects  in  California. 


Fig.  1.— The  Black  Scale  on  Lemon, 


Fig.  2.— The  Red  Scale  on  Lemon. 


Here  was  tried  the  generation  of  the  gas  in  a  simple  generator  be- 
neath the  tent,  and  the  production  of  the  gas  according  to  the  formula 
now  in  use,  and  better  results  were  obtained  than  had  hitherto  been 
known.  Both  Mr.  Coquillett  and  Mr.  Bishop  claim  to  have  originated 
the  changes,  but  we  will  not  attempt  to  decide  where  the  honor 
belongs. 

All  who  had  tried  fumigation  had  noticed  that  the  trees  were  more 
injured  during  the  middle  of  the  day  than  at  other  times,  and  it  was 
usually  attributed  to  the  heat  in  some  way  causing  the  gas  to  act  on 
the  foliage;  but  at  this  time  Mr.  Coquillett  began  to  work  on  the 
theory  that  it  was  the  actinic  rather  than  the  heat  rays  of  the  sun  that 
produced  this  effect,  and  a  black  tent  was  used  in  the  work  on  Mr. 
Bishop's  place,  which  confirmed  him  in  this  idea.  The  idea  seems  to 
have  been  first  suggested  by  Mr.  Bishop,  judging  from  the  subsequent 
decision  of  the  Commissioner  of  Patents,  though  Mr.  Coquillett  claims 
to  have  originated  it.  At  any  rate  Mr.  Bishop  was  the  first,  who, 
acting  on  this  theory,  inaugurated  night  work,  upon,  as  he  claims, 
the  suggestion  of  his  wife;  but  Mr.  Coquillett  claims  to  have 
stated  to  Mr.  Bishop  that  better  results  would  be  obtained  by  night 
work.  It  will  not  be  necessary  to  enter  further  into  this  controversy, 
and  it  will  be  sufficient  to  point  out  that  at  that  time  in  the  orchard  of 
Mr.  Bishop  there  were  originated  three  items  that  form  the  foundation 
of  the  present  practice  of  fumigation  in  California,  the  formula,  the 
method  of  generating,  and  the  night  work. 

Whether  the  theory  upon  which  night  work  was  tried  is  correct  or 
not  it  would  be  difficult  to  decide,  but  in  practice  such  uniform  and 
satisfactory  results  have  followed  its  adoption  that  it  is  regarded  as 
essential  to  good  fumigation.  The  success  of  the  idea,  and  the  council 
of  his  neighbors,  led  Mr.  Bishop,  in  company  with  them,  to  apply  for 
a  patent,  which  was  granted  in  spite  of  the  vigorous  protests  of  Mr. 
Coquillett  and  Professor  Riley,  communicated  to  the  Commissioner  of 
Patents  by  the  Assistant  Secretary  of  Agriculture.  The  courts,  how- 
ever, later  declared  the  process  unpatentable,  and  thus  ended  the 
second  attempt  to  control  the  process  for  profit. 


The  Tent. — At  first  there  was  a  great  deal  of  diversity  in  the 
construction  of  the  tent  and  the  means  of  manipulating  it.  It  was 
usually  some  form  of  bell  shape,  and  generally  constructed  of  bed  tick- 
ing, oiled  after  making. 

The  Wolfskill  fumigator  was  a  bell  tent  manipulated  by  a  derrick 
mounted  on  a  wagon,  and  having  an  arm  on  each  side  extending  over 
the  tops  of  the  trees  when  driven  between  the  rows.  The  tent  was 
lifted  by  means  of  a  rope  attached  to  the  top  and  extending  to  a  loop 
at  the  end  of  the  arm  of  the  derrick,  through  which  the  tent  was  drawn 
as  it  was  removed  from  the  tree.  It  is  illustrated  in  the  Report  of  the 
United  States  Department  of  Agriculture  for  1887. 

The  Titus  fumigator  was  a  similar  tent,  but  supported  by  a  large, 
square  frame  with  braced  legs  at  each  corner,  mounted  on  wheels,  and 
with  a  piece  across  the  top,  on  which  the  tent  could  be  wound  in 
removing  it  from  a  tree.     This  is  also  shown  in  the  above-named  report. 

The  Culver  fumigator  consisted  of  two  light  frames  having  the 
shape  of  a  half-bell  and  covered  with  a  cloth,  forming  a  complete 
tent  when  closed  together  around  a  tree.  This  is  also  figured  in  the 
report  mentioned  above,  but  it  was  later  simplified  and  the  cloth 
allowed  to  rest  on  the  sides  of  the  tree. 

These  were  all  provided  with  the  old  generators  with  blowers,  and 
have  all  been  replaced  by  better  tents  as  described  below  in  this 
bulletin. 

The  Dose. — Of  fundamental  importance  is  the  quantity  of  chemi- 
cals to  be  used.  This  has  been  a  matter  of  considerable  variation,  and 
because  of  its  importance  will  be  discussed  quite  fully.  The  original 
table  given  by  Morse,  but  with  the  addition  of  a  column  giving  the 
amount  of  dry  cyanide,  is  as  follows: 


Size  of 

Cyanide  of 

(Equivalent  to 

Bi-Carbonate 

Sulphuric 

Tree. 

Potassium. 

Dry  Cyanide.) 

of  Soda. 

Acid. 

Feet. 

Fluid  Ounces. 

Ounces. 

Pounds. 

Fluid  Ounces. 

4 

.7 

.28 

.05 

.4 

5 

1.6 

.64 

.11 

.9 

6 

2.5 

1.0 

.20 

1.3 

7 

4.0 

1.6 

.29 

2.1 

8 

6.0 

2.4 

.44 

3.1 

9 

8.5 

3.4 

.63 

4.5 

10 

11.5 

4.6 

.87 

6.2 

11 

15.5 

6.2 

1.14 

8.2 

12 

20.0 

8.0 

1.50 

11.6 

13 

25.4 

10.16 

1.90 

13.5 

14 

31.6 

12.64 

2.50 

16.6 

15 

39.2 

16.48 

2.92 

20.7 

16 

47.5 

19.0       . 

3.55 

25.2 

17 

57.5 

23.0 

4.23 

30.1 

18 

67.7 

27.08 

5.05 

35.8 

19 

70.9 

28.36 

5.93 

42.1 

20 

90.5 

36.2 

6.93 

49.2 

The  latter-half  of  the  table  is  by  no  means  accurately  calculated, 
and  is  probably  safest  between  eight  and  twelve  feet.  The  table  was 
calculated  for  trees  about  as  broad  as  high,  such  as  naval  oranges. 


8 


Mr.  Coquillett  gave  the  same  year  the  following  amounts  of  chemicals: 


In  Dry  Ga 

s  Process. 

Height 

Diameter 

Cyanide 

Sulphuric 



(Equiv.  to 

of  Tree. 

of  Tree. 

Solution. 

Acid. 
Fluid  Ounces. 

Sulphuric 
Acid. 

Bi-Caebonate 

of  Soda. 

Dry 
Cyanide.) 

Feet. 

Feet. 

Fluid  Ounces. 

Fluid  Ounces. 

Ounces. 

Ounces. 

6 

5 

2 

li 

If 

H 

li 

10 

10 

12 

7 

11 

11 

n 

12 

8 

9 

5 

8 

8 

3i 

16 

12 

28 

16 

25 

27 

m 

20 

14 

47 

26 

40 

43 

* 

We  do  not  understand  exactly  the  method  of  calculating  this  table, 
but  it  uses  distinctly  more  chemicals  than  the  previous  one.  These 
are  the  tables  given  in  the  Report  of  the  State  Board  of  Horticulture, 
printed  in  1888. 

In  1889,  Mr.  Coquillett  gave  another  table,  according  to  the  new 
formula  developed  by  the  work  in  Orange  County,  and  is  the  first  one 
for  that  formula.     The  table  is  as  follows: 


Height  of 

Diameter  of 

Cyanide  of 

Water. 
Fluid  Ounces. 

Sulphuric 

Tree. 

Tree. 

Potassium. 

Acid. 

Feet. 

Feet. 

Ounces. 

Fluid  Ounces. 

10 

8 

2i 

41 

2i 

12 

10 

41 

9 

4*. 

12 

14 

81 

m 

81 

14 

10 

54 

ii 

51 

14 

12 

n 

15 

1\ 

16 

14 

12 

24 

12 

18 

14 

15 

30 

15 

The  amounts  given  in  this  table  are  from  a  quarter  to  a  third  less 
than  for  the  former  process,  and  somewhat  less  than  the  Morse  table. 

The  next  table  to  appear  was  the  one  given  by  Mr.  Craw  in  his 
pamphlet  on  Destructive  Insects,  and  is  as  follows: 


Height  of 
Tree. 

Diameter 

THROUGH 

Foliage. 

Water. 

Sulphuric 
Acid. 

Cyanide  of 
Potassium. 

Feet. 

Feet. 

Fluid  Ounces. 

Fluid  Ounces. 

Ounces. 

6 

4 

2 

1 

1 

8 

6 

4 

2 

2 

10 

8 

6 

3 

3 

12 

10 

10 

5 

5 

12 

14 

14 

7 

7 

14 

14 

16 

8 

8 

16 

16 

18 

9 

9 

18 

16 

20 

10 

10 

20 

16 

22 

11 

11 

22 

18 

24 

12 

12 

24 

20 

26 

13 

13 

26 

20 

27 

m 

134 

30 

20 

28 

14 

14 

This  table  is  the  most  faulty,  in  its  calculations,  of  any  that  have 
appeared,  for  the  amounts  of  chemicals  given  varies  as  the  vertical 
section  of  the  tent  and  not  as  its  cubical  contents.  It  is,  therefore, 
much  too  strong  for  the  smaller  trees  and  too  weak  for  the  larger. 

Mr.  T.  B.  Johnson,  who  superintended  the  fumigation  work  of  the 
San  Diego  County  Horticultural  Board,  adopted  a  table  which  appeared 
in  the  report  of  the  State  Board  of  Horticulture  for  1894,  as  follows: 


Height  of 
Tree. 

Diameter 
through 
Foliage. 

Water. 

Sulphuric 
Acid. 

Cyanide  of 
Potassium. 

Feet. 

Feet. 

Fluid  Ounces. 

Fluid  Ounces. 

Ounces. 

6 

4 

3 

li 

1 

8 

6 

6 

21 

2 

10 

8-10 

12-15 

4-5 

31-  41 

12 

10-14 

18-26 

6-8f 

5-7 

14 

12-14 

26-30 

81-10 

7-8 

16 

14-16 

33-37 

11  -121 

9  -10* 

20 

16-18 

48-56 

16  -18f 

13  -15 

24 

18-20 

67-75 

221-25 

18  -20 

This  table  is  based  on  the  preceding  one,  indeed  is  practically  the 
same,  but  contains,  as  stated,  increased  doses  for  the  larger  trees  where 
the  former  table  was  most  in  error.  The  plan  of  calculating  both 
tables  is  entirely  wrong;  and  it  is  not  strange  that  with  this  table  to 
follow,  fumigation  should  have  fallen  into  some  disrepute  in  San 
Diego  County. 


In  Bulletin  No.  115  of  this  Station  the  following  table  is  given: 

Height 

of  Tree. 

Amount  of  Cyanide  of  Potassium. 

If  as  broad  as 
high  (Navel 
Oranges,  etc.) 

6  feet. 

8  feet. 
10  feet, 
12  feet. 
15  feet. 
19  feet, 

If  §  as  broad  as 
high  (Seedling 
Oranges,  etc.) 

1  ounce 

1  ounce 

2  ounces       

4  ounces  

8  ounces 

1  pound 

8  feet, 
10  feet. 
12  feet. 
15  feet, 
20  feet. 
28  feet. 

The  calculation  of  the  above  table  is  correct,  but  the  amounts  given 
are  altogether  below  the  present  practice  of  most  California  fumigators; 
some,  including  the  most  successful,  use  nearly  twice  as  much.  It 
was  not  prepared  as  the  result  of  original  work,  but  rather  as  a 
re-calculation  of  the  average  of  the  two  preceding  tables. 

The  latest  table  that  has  been  published  is  that  calculated  by 
Professor  Johnson  of  the  Maryland  Station,  based  on  his  work  on  the 
San  Jose  scale.     It  is  as  follows: 


10 


Height  op  Tree. 

Diameter. 

Cyanide. 

Acid. 

Water. 

Feet. 

Feet. 

Grams. 

Ounces. 

Ounces. 

4 

3 

6.17 

.32 

.48 

5 

4 

12.82 

.67 

1 

6 

4 

18.85 

1 

1.05 

7 

4 

26.75 
Ounces. 

1.41 

2.11 

7 

5 

1.11 

1.66 

2.49 

8 

4 

1.30 

1.95 

2.92 

8 

5 

1.50 

2,25 

3.39 

9 

5 

1.96 

1.94 

4.41 

9 

6 

2.24 

2.36 

5 

10 

7 

3.20 

4.08 

7.02 

10 

8 

3.62 

5.43 

8.14 

11 

7 

3.95 

5.92 

8.88 

11 

8 

4.40 

6.60 

9.90 

12 

9 

5.88 

8.82 

13.23 

12 

10 

6.51 

9.76 

14.65 

13 

9 

6.93 

10.39 

15.58 

13 

10 

7.65 

11.47 

17.26 

14 

11 

9.76 

14.64 

21.96 

14 

12 

10.65 

15.97 

23.45 

15 

11 

13.28 

16.42 

29.88 

15 

12 

14.24 

21.36 

32.04 

16 

14 

16.34 

24.51 

36.76 

16 

15 

17.53 

26.27 

39.43 

17 

14 

18.39 

27.57 

41.35 

17 

15 

19.36 

29.40 

44.23 

18 

15 

22.06 

33.09 

49.63 

19 

16 

26.10 

39.15 

58.72 

20 

16 

29 

43.05 

65.25 

The  above  table  is  accurately  made,  but  the  amounts  are  very  much 
greater  than  used  in  this  State. 

In  order  to  compare  the  above  tables,  the  cubic  contents  of  the  tents 
of  the  various  dimensions  given  were  calculated.* 

The  following  table  gives  the  results  thus  obtained: 


Date. 

Name. 

Capacity  per  Ounce  of  Cyanide. 

1887 

F.  W.  Morse 

145  cubic  feet 

1888 

D.  W.  Coquillett 

95  cubic  feet 

1889 

D.  W.  Coquillett 

165  cubic  feet 

1891 

Alexander  Craw 

352  cubic  feet 

1894 

T.  B.  Johnson 

242  cubic  feet 

1896 

C.  W.  Wood  worth 

300  cubic  feet 

1898 

W.  G.  Johnson 

80  cubic  feet 

It  is  interesting  to  notice  that  the  best  practice  in  this  State  at  the 
present  time  is  scarcely  at  all  different,  in  the  amount  of  cyanide  used, 


*  The  manner  of  calculation  is  as  follows :  The  top  portion  of  the  tent  was  considered  a  hemi- 
sphere and  the  lower  portion  a  cylinder.  The  formula  is  7T  r2  (h—hr)  in  which  h  is  the  height  of  the 
tent  and  r  one-half  of  the  diameter.  The  average  capacity  of  the  tents  in  each  table  was  thus 
determined  and  compared  with  the  average  dose. 


11 

from  the  formula  originally  published  by  Mr.  Morse  in  Bulletin  71  of 
this  Station. 

The  Present  Practice. 

Having  followed  the  changes  through  which  the  process  has 
passed,  we  must  consider  in  detail  the  apparatus  and  plan  of  procedure 
used  at  the  present  time.  There  is,  of  course,  no  absolute  uniformity, 
for  every  outfit  is  made  or  handled  in  a  somewhat  different  manner  in 
some  of  its  details. 

The  Canvas. — Common  duck  is  now  uniformly  employed  for  mak- 
ing the  tent,  most  of  them  being  made  of  the  8-ounce  canvas,  such  as 
is  used  for  light  sails.  The  cloth  is  lapped  and  double-sewed  in  the 
same  manner  as  for  tents  or  sails.  The  edge  is  usually  simply 
hemmed,  but  some  bind  it  with  rope.  Whenever  permanent  rings  for 
handling  are  attached,  the  tent  is  reinforced,  but  this  is  a  matter  in 
which  there  is  much  diversity.  The  details  of  the  construction  will 
depend  somewhat  on  the  size  and  kind  of  tent,  and  will  be  referred  to 
again,  below. 

After  the  tent  is  made,  it  is  treated  in  some  manner  to  make  it 
gas-tight,  so  as  to  confine  the  gas  better.  Three  methods  are  used  for 
this  purpose,  all  of  which  seem  to  give  good  satisfaction. 

The  first  method  is  to  thoroughly  treat  the  tent  with  boiled  linseed 
oil.  It  is  applied  freely  with  a  brush,  and  the  whole  cloth  becomes 
saturated  with  it.  The  tent  must  be  kept  spread  out  till  quite  dry, 
for  the  oil  has  a  great  tendency  to  heat  if  not  exposed  freely  to  the 
air,  and  the  cloth  chars  and  becomes  rotten.  If  properly  done,  the  tent 
remains  strong  and  tight,  and  is  not  too  stiff. 

The  second  method  consists  in  the  use  of  sizing  and  paint.  The 
sizing  is  applied  in  the  same  manner  as  the  oil,  and  penetrates  the  fiber 
of  the  cloth  in  the  same  way.  As  soon  as  this  coat  is  dry  it  is 
followed  by  another  of  rather  thin  flexible  paint,  sometimes  on  both 
sides;  the  result  being  a  perfectly  tight  tent  with  a  very  smooth  sur- 
face and  fully  as  flexible  as  the  oiled  tent.  The  sizing  protects  the 
fiber  of  the  cloth,  so  there  is  no  danger  of  heating. 

The  third  method  is  the  saturation  of  the  cloth  by  a  decoction  of 
the  chopped-up  leaves  of  the  common  prickly  pear  cactus  {Opuntia 
engelmani.)  This  decoction  is  made  by  filling  a  barrel  two-thirds  full 
of  the  chopped  stems,  adding  cold  water  till  the  barrel  is  nearly  full; 
then  letting  it  soak  twenty-four  hours,  when  it  is  drawn  off  and 
strained,  and  is  ready  for  use.  This  decoction  is  seldom  used  by 
itself,  but  other  substances  are  added  according  to  the  whim  of  the 
person  treating  the  tents.  Very  generally  a  pigment,  like  yellow  ochre 
or  Venetian  red,  is  added  to  give  more  body  to  the  mixture;  sometimes 
glue  is  added  also.  There  is  some  tendency  in  tents  treated  with  the 
cactus  decoction,  to  become  moldy  when  not  in  use,  to  prevent  which 
some  prepare  a  tannin  solution  to  add  to  the  mixture.  The  decoction 
may  be  applied  to  the  tents  with  a  brush,  but  a  better  way  is  to  soak 
them  during  the  night  in  a  trough  containing  the  mixture.  In  the 
morning  they  can  be  raised  by  means  of  ropes  and  pulleys  and  allowed 
to  drain  for  some  time  and  then  spread  out  to  dry.  Tents  treated 
with  this  mixture  are  scarcely  at  all  stiffened  and  seem  to  be  satisfac- 
torily tight. 


12 


The  Bell  Tent. 


The  tents  known  as  bell  tents  are  cylindrical  in  shape,  with  the  top 
ronnded  over  like  a  dome.  They  are  used  in  connection  with  a  der- 
rick, by  means  of  which  they  are  placed  upon  and  lifted  from  trees; 
the  derrick  also  supports  the  weight  of  the  tent  while  it  is  upon  the 
tree.  The  bell  tent  was  one  of  the  original  forms  of  tents,  and  while 
mostly  supplanted  by  other  styles,  is  still  used  to  a  considerable  extent, 
especially  for  very  large  trees.  It  is  the  only  form  of  tent  now  in  use 
where  the  whole  weight  of  the  tent  is  not  carried  by  the  tree,  and 
many  favor  it  for  this  reason. 

The  derrick  used  with  the  bell  tents  at  the  present  time  is  that  used 
with  the  Preble  fumigator,  or  some  modification  of  it.  This  is  shown 
in  Fig.  3.     It  consists  of  a  wagon,  which  supports  a  mast  considerably 

The  Bell  Tent. 


Fig.  3. — Derrick  with  one  tent  nearly  in  place  on  a  tree, 
and  the  other  drawn  up  ready  for  moving. 

higher  than  the  trees  to  be  fumigated,  and  is  braced  at  the  bottom  with 
stays  that  hold  it  rigidly  in  place.  Across  the  top  of  the  mast  a  yard 
is  fastened  and  braced  with  trusses  extending  from  the  mast.  The 
length  of  the  yard  is  about  a  third  longer  than  the  distance  between 
the  rows  of  trees.  Near  each  end  of  the  yard  are  placed  cross-bars  as 
shown  in  the  illustration.  The  arrangement  of  the  ropes  can  be  under- 
stood from  a  study  of  the  figure. 

The  heaviest  rope  is  attached  to  the  top  of  the  tent  with  double 
pulleys.  Along  the  lower  edge,  on  the  four  sides  of  the  tent,  are 
fastened  boards,  generally  of  ordinary  six-inch  fencing,  which  are 
called  trail  boards,  and  from  the  center  of  each  of  these  the  trail 
ropes  pass  upwards  and  over  pulleys  attached  to  the  yard  and  ends 
of  the  cross-bars.  All  these  ropes  follow  the  yard  till  near  the  mast, 
then  passing  again  over  pulleys,  they  go  down  to  the  bed  of  the 
wagon  and  are  fastened  over  belaying  pins.     The  trail   ropes  pass 


13 

through  thimbles  along  the  side  of  the  tent  as  well  as  through  the 
pulley  at  the  center  of  the  trail,  so  that  when  the  latter  is  drawn  up  to 
the  yard  or  cross-bars,  the  sides  of  the  tent  are  gathered  in  three  or 
four  places  and  raised  almost  as  high.  The  only  other  ropes  are  the 
guide  lines  attached  to  the  center  of  the  trails  and  hanging  free.  They 
are  of  such  length  as  to  reach  the  ground  when  the  tent  is  elevated. 

The  manipulation  of  these  tents  can  be  readily  understood  from  a 
study  of  the  engraving.  While  the  tree  is  being  fumigated  the  tent  is 
usually  allowed  to  rest  partly  on  the  tree,  and  not  drawn  up  to  the 
yard  as  shown  in  the  illustration.  Two  persons  can  handle  the 
apparatus,  but  three  or  four  greatly  facilitate  the  work.  The  pro- 
cedure in  changing  the  tent  is  as  follows:  Supposing  that  both  tents 
are  upon  the  trees  and  the  time  has  arrived  to  make  the  change,  the 
first  operation  is  to  pull  on  the  main  rope  attached  to  the  center  of  the 
tent  and  raise  this  as  far  as  it  will  go  easily,  and  then  fasten  the  rope 
again  to  the  belaying  pin.  If  short-handed,  one  tent  is  raised  at  a 
time,  but  with  plenty  of  help  both  go  up  at  the  same  time.  The  trail 
ropes  are  next  taken  in  hand  and  pulled  all  together,  and  if  this  be- 
comes difficult,  two  (or  even  one  at  a  time)  are  pulled  until  the  tent 
on  all  sides  is  pulled  up  to  the  yard  and  cross-bars.  While  this  is 
going  on  one  person  (or  perhaps  more)  is  kept  busy  seeing  that  the 
tent  is  clearing  the  tree  properly.  His  first  business  is  to  see  that  the 
edge  with  the  trail  boards  is  not  caught  inside  of  the  tent;  it  should  slip 
up  around  outside  of  it.  Later  he  will  be  occupied  with  making  the 
tent  slip  off  the  projecting  branches.  He  can  generally  do  this  by 
pulling  on  the  guide  lines,  but  on  very  large  trees  he  may  find  a  light 
ladder  necessary.  The  removal  of  the  tent  would  be  comparatively 
easy  but  for  the  work  at  the  ropes.  After  all  the  ropes  are  pulled  tight, 
including  the  main  rope,  and  both  tents  are  against  the  yard,  the 
apparatus  is  ready  to  shift  to  the  next  row.  The  wagon  may  be  pulled 
along  by  hand,  or  by  a  horse  hitched  to  the  end  of  the  tongue.  If  the 
ground  is  a  little  uneven,  the  apparatus  can  be  kept  from  tipping  over 
by  steadying  it  with  the  guide  lines.  Arriving  at  the  proper  position 
between  the  next  two  trees,  the  first  thing  is  to  arrange  the  guide 
lines  in  their  places  around  the  tree.  The  trail  ropes  are  now  released 
and  the  tent  is  allowed  to  slowly  descend  upon  the  tree.  While  this  is 
taking  place,  one  or  more  are  busy  with  the  guide  lines,  pulling  the 
trail  boards  this  or  that  way  as  may  be  necessary  to  clear  the  branches. 

If  a  branch  is  particularly  spreading  it  may  be  necessary  to  use  a 
ladder,  forcing  it  within  the  tent  by  hand.  Should  the  trees  be  very 
large  the  branches  will  extend  over  the  wagon,  causing  much  trouble 
in  pulling  the  tent  down  on  that  side.  With  a  small  symetrically 
shaped  tree  the  tent  can  be  lowered  rapidly  into  place  without  any 
trouble  whatever.  After  the  trail  ropes  are  all  played  out,  the  main 
rope  is  loosened  and  the  tent  allowed  to  settle  to  the  position  desired, 
and  fastened  there.  There  yet  remains  the  job  of  seeing  that  the 
tent  is  tight  to  the  ground  on  all  sides.  The  trail  boards  are  made  to 
lie  on  the  part  of  the  tent  that  is  on  the  ground,  and  earth  is  thrown  on 
any  part  of  the  edge  of  the  tent  that  does  not  lie  down  well.  When 
both  tents  are  thus  in  position  they  are  ready  for  the  "fumigator,"  or 
man  who  charges  the  generator. 


14 


The  Hoop  Tent. 

The  form  most  used  in  this  State  is  the  hoop  tent,  which  is  a  devel- 
opment from  the  bell  tent  and  is  of  the  same  general  shape.  The 
hoop  was  first  used  as  a  means  of  keeping  the  mouth  of  the  bell  tent 
open,  but  it  was  soon  discarded  in  favor  of  the  trail  boards.  It  was, 
however,  discovered  that  for  rather  small- sized  tents  the  hoop  afforded 
a  better  means  of  handling  than  did  the  derrick. 

The  Small  Hoop-Tent. 


Fig.  4.— Throwing  the  tent  over  a  tree. 


Fig.  5. — Pulling  down  the  tent. 


15 


Fig.  6. — Ready  for  the  Furnigator. 

The  hoop  tents  now  in  use  range  from  eight  to  fourteen  feet  in 
diameter.  They  are  made  in  the  same  way  as  a  bell  tent,  omitting, 
however,  the  arrangements  for  suspending  them,  and  possessing,  in- 
stead, a  series  of  cloth  loops  for  attaching  the  hoop  as  is  shown  in  the 
engraving. 

The  hoop  is  usually  made  of  three-quarter-inch  gas  pipe;  half- 
inch  pipe  will  do  for  the  smaller  sizes,  but  it  is  too  weak  for  hoops 
above  ten  feet  in  diameter,  as  it  bends  too  easily  and  soon  becomes 
very  crooked.  To  make  the  hoop,  pipe  is  coupled  together  until  the 
proper  length  is  reached  according  to  the  size  desired,  and  then  bent 
into  shape.  The  union  is  then  made  by  inserting  into  the  ends  a  piece 
of  iron  rod  a  foot  or  less  in  length  and  just  small  enough  to  enter  the 
pipe.  Holes  are  now  drilled  through  the  pipe  and  rod,  and  rivets  are 
inserted,  thus  making  the  joint  fast.  A  coupling  with  right  and 
left-hand  threads  might  be  used  instead  of  the  rod  and  rivets. 


Fig.  7. — Diagram  illustrating  the  method  of  shifting  a  small  hoop  tent  from  one 
tree  to  another.  The  letters  indicate  thexsuccessive  positions  of  the  hoop  as  the 
tent  is  first  thrown  off  of  one  tree  on  to  the  ground,  and  then  is  picked  up  and  put 
over  the  next. 


16 

The  manipulation  of  a  hoop  tent  varies  according  to  its*  size. 
When  the  diameter  of  a  tent  is  not  much  greater  than  the  distance  be- 
tween the  nearest  branches  of  adjacent  trees,  the  procedure  is  that 
illustrated  in  the  preceding  diagram,  Fig.  7,  and  depicted  in  Figs.  4-6. 

To  move  such  a  tent  from  one  tree  to  the  next,  two  men  place 
themselves  on  opposite  sides  of  it,  grasp  the  hoop  and  raise  the  side 
which  is  opposite  the  tree  to  which  they  intend  to  move  it;  they  step 
side- wise,  dragging  the  side  that  is  on  the  ground  closer  to  the  trunk, 
and  the  hoop  will  be  in  about  the  position  indicated  by  A  in  the  dia- 
gram. The  men,  still  holding  the  hoop  as  they  first  grasped  it,  continue 
to  raise  the  free  side  until  it  passes  over  the  top  of  the  tree,  when  it  is 
allowed  to  fall  to  the  ground  between  the  two  trees.  In  falling  the 
hoop  naturally  moves  away  from  the  tree  from  which  it  came,  so  that 
the  cloth  falls  over  the  edge  of  the  hoop,  as  shown  in  the  diagram.  If 
this  does  not  occur,  the  tent  is  pulled  into  that  position  in  order  that, 
when  the  hoop  is  raised,  the  center  of  the  tent  will  be  brought  at  once 
to  about  the  center  of  the  top  of  the  tree. 

The  men  now  grasp  the  hoop  again,  as  before,  carry  it  towards 
the  tree  and  lift  up  the  further  edge,  then  with  one  movement 
throw  it  over  the  tree  to  about  the  position  indicated  by  D.  Often 
it  will  go  clear  to  the  ground  and  needs  no  further  attention.  If  it 
stays  at  D,  the  men  proceed  to  the  point  highest  from  the  ground,  and 
pull  on  the  hoop  and  canvas  until  the  former  rests  easily  on  the 
ground.  The  cloth  which  extends  beyond  the  hoops  forms  a 
sufficiently  tight  contact  with  the  ground  if  the  latter  is  ordinarily  level. 

The  manipulation  of  the  large  hoop-tents  differs  from  that  above 
described,  from  the  fact  that  the  proximity  of  the  trees  makes  it 
impracticable  to  lay  the  tent  on  the  ground.  The  procedure  in  this 
case  is  indicated  in  the  accompanying  diagram,  Fig.  12,  and  by  Figs. 

8-11. 

The  Large  Hoop-Tent. 


:; 


X 


Fig.  8. — Putting  the  tent  on  a  tree.     The  tent  in  this  case  is  being 
lifted  from  the  ground,  and  not  shifted  from  another  tree. 


17 


The  Large  Hoop- Tent. 


**ip— V 


Fig.  9.— Pulling  down  the  canvas  so  that  the  hoop 
will  rest  freely  on  the  ground. 


Fig.  10. — Beginning  to  raise  the  tent. 


18 


The  Large  Hoop-Tent. 


Fig.  11. — Tent  almost  off  the  tree. 


■S  *0  J&bL 


I 


_I 


\d 


-"     "E 


Fig.  12. — Diagram  illustrating  the  method  of  shifting  a  large  hoop-tent  from  one 
tree  to  another.     The  letters  indicate  the  successive  positions  of  the  hoop. 

It  is  better  to  have  three  men  to  handle  these  tents,  though  two  can 
do  it.  When  working  three,  two  take  hold  in  the  same  way  as 
described  above  for  the  small  hoop-tents,  and  the  third  pulls  on  the 
side  that  is  raised  to  the  position  A.  The  latter  then  catches  the  hoop 
with  a  fork  at  the  end  of  a  pole,  and  as  the  others  lift  he  assists  by 
pushing.     This  is  shown  in  Figs.  10,  11. 

When  the  hoop  has  taken  about  the  position  shown  at  B,  in  Fig. 
12,  or  a  little  past  that  point,  the  two  men  holding  the  sides  of  the  tent 
carry  it  to  the  next  tree  to  the  position  C,  and  then  without  pausing, 
and  while  the  tent  is  full  of  air  and  streaming  out  behind  with  the  aid 
of  momentum  acquired,  the  upper  edge  of  the  hoop  is  forced  over  the 
top  of  the  tree  and  down  on  the  other  side.     Generally  it  is  possible  to 


19 

throw  the  hoop  into  the  position  D,  when  it  can  readily  be  pulled  down 
to  the  ground. 

If  there  is  any  trouble  in  pulling  the  cloth  over,  the  third  man,  hav- 
ing tossed  his  pole  to  the  next  tent,  goes  around  to  the  near  side  of  the 
tent  just  moved,  and  as  the  others  pull  on  the  far  side,  shakes  the 
cloth  of  the  tent  away  from  the  tree,  thus  relieving  some  of  the  friction. 
The  weight  of  the  hoop  of  these  large  tents  greatly  helps  in  the  pro- 
cess of  slipping  the  cloth  over  the  tree,  the  most  energy  being  required 
in  removing  the  tent.  The  large  tents  are  moved  quite  as  rapidly  as 
are  the  smaller  ones.  It  will  be  noticed  that  the  cloth  is  turned  inside 
out  with  each  change  in  the  case  of  the  larger  tents,  but  with  the 
smaller  ones  the  same  side  of  the  cloth  is  always  next  to  the  tree. 

The  Box  Tent. 

The  latest  development  along  this  line  is  what  is  known  as  the  box 
tent.  It  is  an  Eastern  idea  devised  for  use  on  deciduous  trees  in 
which  the  wood  is  less  pliable  and  more  easily  broken  than  are  citrus 
trees.  It  may  deserve  a  trial  in  our  orchards,  though,  doubtless,  we 
would  soon  simplify  the  handling  so  as  to  work  more  rapidly  than  is 
now  possible. 

The  box  tent  is  somewhat  intermediate  between  the  bell,  or  hoop 
tent,  and  a  sheet  tent.  It  has  something  of  the  shape  of  the  hoop 
tent,  but  flaring  beneath  and  without  anything  stiff  at  the  bottom.  It 
is  made  with  a  square  top-piece  and  with  four  sides,  which  are  a  half 
larger  at  the  bottom  than  at  the  top. 

The  manipulation  of  this  tent  is  accomplished  by  the  use  of  a  pole 
called  the  "lifter."  This  pole  has  a  piece  of  scantling  fastened  to  the 
bottom  and  braced,  as  shown  in  Fig.  13,  and  in  the  accompanying 

The  Box  Tent. 


7  ",M 


'M  ~  *  -  *l» 


mm* 


t4^f)t/iili 


Fig.  13. — Lifter  in  position  over  a  tent  ready  to 
remove  it  from  the  tree. 


20 


diagram,  Fig.  14.  To  the  top  of  the  pole  is  attached  a  guy  rope  and 
a  block  pulley  over  which  passes  a  rope  for  lifting  the  tent.  A  small 
Y  at  a  convenient  height  for  fastening  the  rope  completes  the  lifter. 

F 


Fig.  14. — Diagram  illustrating  the  method  of  changing  a  box  tent  from  one  tree 
to  another  by  the  use  of  the  lifter.  A,  B,  C,  D,  and  E  represent  the  successive 
positions  of  the  tent.  F  the  lifter  and  G  guy  rope.  F'  G'  the  second  position  of 
the  same. 

In  changing  the  tent  from  one  tree  to  another  the  process  is  to 
place  the  lifter  next  to  the  tree  to  be  uncovered.  The  guy  rope  is 
then  tied  to  an  adjacent  tree  in  such  a  manner  as  to  allow  the  end  of 
the  lifter  to  stand  over  the  center  of  the  tent.  The  end  of  the  lifter 
rope  is  fastened  to  the  edge  of  the  tent  opposite  the  base  of  the  lifter. 
As  the  edge  of  the  tent  is  being  lifted  by  this  rope,  assistants  pull  the 
edge  of  the  tent  aside,  freeing  the  branches;  small  forked  poles  are 
used  to  assist  in  this  work.  After  all  the  branches  are  free  the  tent  is 
lowered  to  the  ground  beside  the  tree. 

The  lifter  is  now  moved  to  the  tree  to  which  the  tent  is  to  be 
placed,  as  shown  at  C.  By  pulling  on  the  lifter  rope,  the  edge  of  the 
tent  is  raised  again  to  the  top  of  the  pole,  when  the  rope  is  fastened. 
Two  persons  now  take  hold  of  the  edges  of  the  tent  and  pull  them 
around  the  tree,  while  a  third  pulls  on  the  guy  rope  till  the  top  of  the 
tent  is  over  the  top  of  the  tree,  when  the  tent  is  lowered  and  pulled 
into  position.  The  movement  of  the  lifter  by  means  of  the  guy  rope 
is  not  indicated  in  the  drawing,  but  can  be  readily  understood  with- 
out.    The  same  movement  is  useful  in  untenting  a  tree. 

After  letting  the  tent  down  over  the  tree  the  lifter  rope  is  untied 
and  the  bottom  of  the  tent  pushed  up  towards  the  tree  and  made  to  lie 
close  to  the  ground.     If  necessary,  a  little  earth  is  thrown  upon  it  to 

hold  it  down. 

The  Sheet  Tent. 

The  form  that  seems  most  likely  to  replace  all  others  is  the  sheet 
tent.  It  is  the  simplest  to  make,  the  most  readily  adaptable  to  all  sizes 
of  trees,  and  is  almost  as  readily  moved  from  tree  to  tree  as  the  hoop 
tent.  It  contains,  however,  a  great  deal  of  useless  canvas,  which  is  an 
objection  to  the  economical  mind. 


21 

Sheet  tents  are  made  either  in  a  regular  or  in  an  ova.1  hexagon,  and 
perfectly  flat.  A  pair  of  rings  is  often  attached  on  each  side,  near 
what  is  intended  as  the  front  edge;  it  is  convenient  to  attach  these 
rings  by  iron  links,  so  that  they  can  be  rattled  and  found  in  the  dark 
by  shaking  the  tent. 

The  movement  of  the  tent  is  accomplished  by  the  use  of  two  poles. 
These  are  usually  simple  poles  with  a  small  rod  projecting  from  the 
upper  end,  over  which  the  ring  of  the  tent  is  slipped,  a  rope  is  also 
fastened  at  the  upper  end.  The  length  of  the  pole  is  slightly  greater 
than  the  height  of  the  trees  it  is  desired  to  cover.  Sometimes  the  pole 
has  the  same  shape  as  the  lifter  used  for  the  box  tents,  but  the  pulleys 
and  guy  ropes  are  not  needed,  except  for  the  largest  trees. 

The  ordinary  process  of  moving  the  sheet  tent  is  shown  in  Figs. 
16-19  and  by  the  accompanying  diagram  Fig.  15.     A  bird's-eye  view 


'      IvtfS' 


h    1 


.!__, 


m 


Fig.   15.— Diagram  illustrating  the  method  of  shifting  a  sheet  tent  from  one  tree 
to  another.     The  letters  represent  the  successive  positions  of  the  end  of  the  pole. 

The  Sheet  Tent. 


Fig.  16.— Beginning  to  lift  the  edge  of  the  tent. 


99 


The  Sheet  Tent. 


Fig.  17.— Tent  partly  over  the  next  tri 


Pig.  18. — Tree  almost  covered,  pole  falling. 


23 


The  Sheet  Tent. 


Fig.   19.— Adjusting  the  bottom  of  the  tent. 

is  also  shown  in  Fig.  20.  The  men  approach  the  tent  to  be  moved, 
poles  in  hand,  and  finding'  the  rings  insert  the  small  rods  at  the  end 
of  the  poles  and  take  a  hitch  with  the  rope  over  the  ring  to  prevent 
the  latter  from  slipping  off.  They  then  proceed  to  the  other  end  of 
their  poles,  which  they  have  placed  even  with  the  trunk  on  opposite  sides 
of  the  tree  to  which  the  tent  is  to  go.  While  taking  this  station  they 
have  not  let  go  of  the  rope,  but  have  held  it  tight  enough  not  to  loosen 
the  tent  ring.  The  next  step  in  the  process  is  to  place  one  foot  on 
the  end  of  the  pole,  to  prevent  it  from  slipping,  and  to  pull  on  the 
rope.  This  will  lift  up  the  edge  of  the  tent  as  shown  at  A  in  Fig.  15. 
As  the  men  continue  to  pull  on  the  rope  the  end  attached  to  the  tent 
moves  through  the  arc  indicated  by  the  line  of  arrows.  As  soon  as  the 
pole  becomes  nearly  enough  upright,  as  not  to  slip  when  the  foot  is 
removed  from  the  end,  the  man  backs  off,  away  from  the  tree,  and 
thus  gets  a  more  direct  pull  on  the  tent  which  by  this  time  has  begun 
to  require  some  considerable  effort.  This  becomes  necessary  also  in 
order  that  the  pull  from  each  side  may  stretch  out  the  front  edge  of 
the  tent  so  that  it  may  clear  the  top  of  the  tree. 

The  tent  is  now  spread  out  over  two  trees  and  reaches  the  ground  on 
either  side.  As  the  men  at  the  ropes  continue  to  back  away  the  tent 
is  slipped  from  one  tree  to  the  next  and  the  poles  fall  to  the  ground. 
In  this  last  stage  in  the  process  care  must  be  taken  that  both  poles 
reach  the  ground  at  about  the  same  time.  If  this  is  not  done  the  tent 
will  shift  to  the  side  of  the  pole  which  first  reaches  the  ground,  and  if 
that  side  is  pulled  very  much  too  fast  the  tent  may  not  reach  the 
ground  on  the  opposite  side,  and  sheet  tents  are  rather  harder  to  adjust 
than  other  kinds.  This  same  difficulty,  in  regard  to  the  front  and  back 
ends  of  the  tent,  often  occurs  when  using  a  tent  barely  large  enough  for 
the  tree .     If  the  tent  is  pulled  too  slowly  the  poles  will  slip  when  the 


24 

tent  is  not  quite  over,  and  the  front  will  not  reach  the  ground;  and  on 
the  other  hand,  if  it  is  pulled  too  rapidly,  the  tent  will  go  too  far,  and 
the  back  end  be  free  from  the  ground.  The  oval  tent  was  made  to 
overcome  this  difficulty,  for  with  it  care  only  need  be  taken  to  slide  the 
tent  far  enough. 

When  using  a  large  tent  for  a  very  small  tree  the  tent  is  pulled  up 
so  as  to  have  sufficient  slack  canvas  to  go  over  the  tree,  and  this  is 
pulled  over  by  hand.  When  being  removed,  the  cloth  is  pulled  back 
in  the  same  manner  as  it  was  put  on,  and  dragged  along  the  ground  to 
the  next  tree. 

In  the  case  of  very  large  trees,  which  require  the  lifter  style  of  pole, 
the  process  is  as  follows:  The  poles  are  set  up  and  the  guy  ropes 
attached  as  described  for  the  box  tent,  only  that  two  poles  are  used. 
The  other  ropes  are  now  attached  to  the  tent  at  the  near  edge  and  the 
latter  pulled  to  the  top  of  the  pole.  The  rope  is  then  made  fast,  the 
guy  ropes  pulled,  and  the  tent  slid  in  the  same  manner  as  with  smaller 
tents.  Sometimes  the  pole  is  not  set  at  such  an  angle  but  nearer  the 
tent,  when  it  will  be  necessary,  after  sliding  the  tent  part  of  the  way, 
to  again  tie  the  guy  rope  and  lift  the  bottom  of  the  pole  over;  it  will 
then  be  opposite  the  trunk,  and  the  tent  will  be  lifted  high  enough 
when  it  is  given  the  final  shift. 

When  there  is  fear  of  breaking  the  branches  in  removing  a  tent, 
the  practice  is  to  "skin  it  off,"  using  a  pole  of  the  lifter  pattern, 
and  carry  the  rope  around  to  the  far  side  and  attach  it  to  the  edge 
of  the  tent  there.  The  tent  by  this  method  slides  over  itself  and 
saves  the  tree  to  that  extent;  it  is  pulled  over  on  to  the  next 
tree  as  in  the  preceeding  methods.  Since  much  of  the  tent  by  this 
method  falls  to  the  ground,  it  is  harder  on  the  tree  while  it  is  being 
tented.     By  this  process  the  tent  is  reversed  each  time  it  is  changed. 

Procedure. 

The  cost  of  fumigation,  and  therefore  the  profit  in  its  use, 
depends  in  a  great  measure  upon  the  arrangement  of  details, 
especially  in  the  economical  use  of  time.  This  is  more  important 
than  in  the  case  of  most  methods  for  killing  insects,  because  of  the 
time,  forty  minutes,  required  for  the  operation  of  the  gas.  Fumiga- 
tion may  be  economically  done  in  one  of  two  ways;  with  a  small 
outfit  arranged  to  fit  in  with  other  work,  or  with  a  large  number  of 
tents  sufficient  to  keep  all  hands  busy. 

Work  with  a  small  outfit  can  be  arranged  so  as  to  waste  but  little 
time.  Fortunately,  the  tent  may  even  be  left  on  all  night  without 
danger,  if  desired,  so  that  a  strict  record  of  the  time  is  not 
necessary,  only  that  it  be  not  too  short.  A  good  arrangement  is  as 
follows:  The  tents  are  placed  on  at  the  close  of  the  day's  work;  they 
are  changed  after  supper,  and  again  just  before  bed-time,  leaving  them 
on  till  morning,  care  being  taken  to  pull  them  off  before  the  sun  gets  at 
them.     This  will  give  three  fumigations  each  night. 

Large  outfits  are  so  expensive  that  the  owner  generally  feels  like 
keeping  them  in  operation  all  night,  though  some  are  used  only  in  the 
evening.  The  number  of  tents  necessary  will  depend  on  the  size  of 
the  tent  and  the  number  of  the  men.  The  smallest  number  of  men 
that  can  work  to  advantage  is  two;   they  could  handle  perhaps  twenty 


25 

tents  of  medium  size.  This  would  allow  two  minutes  for  each  tent, 
which  ought  to  be  sufficient  to  change  the  tent  and  introduce  the 
chemicals.  It  is  doubtful,  however,  if  the  fumigator  should  take  part 
in  the  vigorous  physical  work  of  changing  the  tents  where  so  much 
depends  on  his  judgment. 

The  number  generally  employed  in  a  fumigating  gang  is  four  or 
five,  according  to  the  size  of  the  trees.  One  man  introduces  the 
chemicals,  another  looks  out  for  the  generator  and  measures  the  acid, 
and  two  or  three  handle  the  tents.  Such  a  gang  can  handle  from 
thirty  to  forty  medium  sized  tents  and  cover  four  to  six  acres  of 
orchard  in  a  night. 

There  is  much  variation  in  the  detail  of  procedure  in  fumigating; 
one  of  the  best  methods  is  illustrated  in  the  accompanying  diagram, 
Fig.  20.     It  is  intended  to  represent  a  gang  of  four  working  with 


Up 


I,   ^«^<r-  / 


^^ 


tm. 


km 


Fig.  20.— Bird's-eye  view  of  a  young  orchard  being  fumigated  under  sheet  tents. 
F  the  Fumigator.  H  the  Helper  who  carries  the  generators  and  measures  the  acid, 
R  and  L  the  tent  men.  The  arrow  lines  indicate  the  path  traversed  by  each  of 
these  parties. 

sheet  tents  in  an  orchard  of  rather  small  trees.  Three  trees  are  shown 
newly  covered,  one  tent  in  the  process  of  being  shifted,  and  three 
others  ready  to  have  the  tents  removed.  The  four  dark  spots  indicate 
the  position  of  the  men  at  the  time  the  fumigator  is  about  to  go  under 
the  tent,  and  the  lines  of  arrows  show  the  paths  over  which  the  men 
will  travel  during  the  next  minute.  The  fumigator  enters  the  tent 
(Fig.  21),  introduces  the  chemicals  and  quickly  withdraws,  sees  that 
the  tent  is  down  tightly  to  the  ground,  and  picks  up  his  tray  of 
cyanide  and  proceeds  to  the  next  tree.     The  helper  holds  up  the  edge 


26 

of  the  tent  while  the  fumigator  enters,  and  drops  it  as  he  comes  out, 
then  turning  he  chirps  to  the  horse  in  the  acid  wagon  and  drives  along 
to  the  next  tree.  He  next  removes  the  generator  from  beneath  this 
tree,  pours  out  the  contents  (already  used)  on  the  ground,  measures 
out  the  water  and  then  the  acid  according  to  the  directions  of  the  fumi- 
gator. (Fig.  22. )  He  then  carries  the  generator  to  the  fumigator  who 
is  waiting  by  the  next  tent. 

The  Acid  Wagon. 


Fig.  21. — The  helper  in  the  act  of  measuring  the  acid  in  a  graduate.  A 
generator  is  shown  on  the  shelf  below  the  water  tank.  The 
torch  is  shown  above  and  between  the  acid  and  water  tanks. 

The  Fumigator. 


Fig.  22. — The  Fumigator  in  the  act  of  charging  a  generator  under  the  hoop  tent. 


27 

The  tent  men  are  shown  in  diagram  (No.  20)  as  they  are  backing  off 
with  the  end  of  the  rope.  They  continue  to  back  off  as  indicated  till 
the  tent  is  over  the  tree,  then  proceeding  to  the  tent  they  adjust  the 
bottom  as  they  pass  around  it,  one  on  either  side.  Proceeding  to  the 
next  tent  they  attach  their  poles,  then  going  to  the  other  end  of  their 
poles,  hold  them  down  with  their  feet  as  they  pull  on  their  ropes  and 
raise  the  edge  of  the  tent.  As  soon  as  the  pole  is  high  enough  they 
back  off,  and  the  ends  of  the  lines  show  the  position  corresponding 
with  that  they  had  at  first.  The  variations  depend  on  differences  in 
the  plan  of  estimation,  and  in  the  kind  of  tent. 

Estimating  the  Dose. — The  responsibility  in  the  whole  process  rests 
on  the  fumigator,  for  he  is  the  one  who  chooses  the  quantity  of  the 
dose;  in  practice  the  amount  prescribed  depends  upon  his  personal 
judgment.  The  fumigator  looks  at  a  tree  and  says  eight  ounces,  six  and 
a  half  ounces  or  ten  ounces  according  to  his  idea  of  its  size.  The  result 
is  that  a  great  deal  of  unsatisfactory  work  is  done.  The  wonder  is,  that 
the  results  are  as  uniform  as  they  are.  There  are  two  ways  of  verify- 
ing one's  judgment  as  to  the  proper  doses  to  be  given.  The  one  most 
commonly  used  is  a  subsequent  inspection  of  the  trees;  the  practice 
being  to  give  a  little  more  gas  than  the  trees  will  stand  without  injury. 
If  the  slight  injury  produced  is  the  same  on  all  the  trees,  the  fumiga- 
tor 's  judgment  is  supposed  to  be  working  normally.  This  is  very 
misleading,  for  the  larger  the  tree  the  greater  the  injury,  if  the  dose  is 
properly  proportional  to  the  cubic  content.  The  reason  for  this  is  the 
difference  in  the  generation  of  the  gas  in  large  quantities,  and  its 
relatively  slower  diffusion  in  a  large  volume. 

The  other  method  is  to  measure  the  tree  and  find  the  amount  of  the 
dose  by  consulting  the  tables.  If  the  tables  are  correctly  calculated 
and  the  measurement  accurately  done,  this  is  a  safe  method,  but  there 
are  grave  difficulties  in  the  way  of  accurately  measuring  a  tree.  If  not 
tented,  it  is  difficult  to  judge  how  much  to  allow  for  the  bending  of  the 
branches  under  the  weight  of  the  tent.  If  tented,  which  is  really  the 
correct  way,  there  are  practical  difficulties  in  measuring  the  diameter 
and  height.  To  simplify  the  measurement  and  estimation  of  a  tent 
the  following  table  is  prepared.  The  center  column  gives  the  various 
doses  corresponding  to  the  sizes  of  trees  given  in  the  columns  on  either 
side.  Those  on  one  side  have  been  calculated  so  as  to  give  three  parts 
of  hydrocyanic  acid  gas  in  1000  parts  of  air  (or  0.3  per  cent.),  on  the 
other  side  two  parts  in  1000  of  air  (or  0.2  per  cent. ) .  For  winter  treat- 
ment for  deciduous  trees  0.3  per  cent,  gas  is  suggested,  and  is  nearly 
the  strength  recommended  in  the  Eastern  states  for  the  San  Jose  scale. 
One-half  of  this  amount  is  not  far  from  the  commonest  practice  in  this 
State  for  the  citrus  trees.  The  0.2  per  cent,  gas  is  suggested  for 
citrus  trees  and  agrees  with  the  amounts  used  by  some  of  the  most 
successful  fumigators,  though  others  get  fair  results  with  scarcely 
more  than  half  this  amount. 

The  measurements  to  be  taken  when  using  this  table  are,  (1)  around 
the  tent,  and  (2)  over  the  tent  from  ground  to  ground.  If  these  two 
measurements  are  about  equal,  as  they  will  be  for  many  orange  trees, 
the  number  nearest  the  measurement  is  found  in  the  circumference 
column,  and  the  corresponding  dose  will  be  seen  in  the  center  column. 


28 


Table  Showing  Doses  Suitable  for  Trees  of  Different  Measurements. 


0.3  Per  Cent.  Gas. 


4  Ounce 
Differential. 

Circumference 
of  Tree. 

Ft. 

In. 

Ft. 

In. 

3 

5 

19 

1 

3 

20 

6 

2 

7 

21 

11 

2 

4 

23 

2 

2 

24 

1 

1 

11 

25 

1 

1 

10 

26 

1 

9 

26 

10 

1 

8 

27 

8 

1 

7 

28 

5 

1 

6 

29 

1 

1 

5 

29 

9 

1 

4 

30 

4 

1 

3 

31 

6 

1 

2 

32 

7 

1 

1 

33 

8 

1 

34 

8 

11 

35 

7 

10 

36 

6 

10 

37 

5 

9 

38 

3 

9 

39 

8 

39 

9 

8 

40 

5 

7 

41 

2 

7 

42 

8 

7 

43 

11 

6 

45 

6 

46 

1 

6 

47 

2 

5 

48 

2 

2 

2i 

3 

31 

4 

4i 

5 

5i 

6 

6* 

7 

n 

8 

9 

10 
11 
12 
13 
14 
15 
16 
17 
18 
19 
20 
22 
24 
26 
28 
30 
32 


0.2  Per  Cent.  Gas. 


Circumference 
of  Tree. 


Ft.  In. 

22  1 

23  7 
25 


26 
27 

28 


29  10 

30  9 

31  8 

32  7 

33  4 
34 

34  8 

36  1 

37  5 

38  7 

39  10 

40  11 

41  11 

42  10 

43  9 

44  8 


45 
46 
47 
48 
50 
51 
52 
54 
55 


h  Ounce 
Differential. 


Ft.  In. 
3  11 
3  4 
2  11 
2  8 
2  6 
2  4 
2  2 
2 

1  10 
1  9 
1  8 
1 
1 
1 
1 
1 
1 


1  1 
1  1 

1 
11 
11 

10 
10 
10 
9 
9 
8 
8 
7 
7 


29 

If  these  two  measurements  are  not  nearly  the  same,  the  outside 
columns  become  of  use,  for  they  show  for  each  size  how  much  differ- 
ence must  occur  to  make  necessary  a  half  ounce  increase  or  decrease 
in  the  dose.  That  is,  for  each  differential  there  must  be  added  or 
deducted  one-half  ounce  of  cyanide.  For  instance,  if  the  difference 
between  the  distance  over  and  around  the  tree  is  5  feet,  and  the  differ- 
ential for  that  circumference  is  3  feet  11  inches,  then  the  dose  must 
be  increased  or  diminished  by  a  little  more  than  one-half  ounce;  but  if 
that  differential  be  1  foot,  then  for  each  foot  there  must  be  added  or 
subtracted  one-half  ounce,  or  2^  ounces  for  the  five  feet. 

As  an  example,  suppose  a  tree  were  35  feet  around  and  36  feet 
over  the  top,  and  a  person  were  using  the  0.2  per  cent,  table :  Running 
down  the  circumference  column  we  find  that  34  feet  8  inches  (the  near- 
est to  35  inches)  requires  8  ounces  and  that  the  differential  is  1  foot 
6  inches,  that  is,  35  feet  requires  a  little  over  8  ounces,  and  the 
difference  between  the  two  measurements  around  and  over  the  tree, 
1  foot,  is  nearly  enough  to  require  another  half  ounce,  so  that  8 h 
ounces  would  be  about  right.  Suppose,  again,  the  distance  around 
a  tree  to  be  40  feet,  and  that  over  the  top  only  35  feet;  using  the  same 
table,  we  find  opposite  39  feet  10  inches  (the  nearest  to  40  feet)  the 
dose  12  ounces.  But  the  distance  over  the  top  is  5  feet  less,  and  a  less 
amount  of  cyanide  will  be  necessary.  We  therefore  use  the  differential 
(1  foot  2  inches)  and  deduct  one-half  ounce  for  each  1  foot  2  inches 
difference,  or  about  2  ounces  altogether.  This  leaves  10  ounces  as 
the  correct  dose  for  this  tree. 

These  measurements  are  not  supposed  to  be  taken  with  every  tree, 
but  in  cases  of  doubt,  and  occasionally  to  correct  one's  judgment;  and 
in  the  case  of  those  beginning  to  fumigate,  whose  judgment  is  not  yet 
developed. 

Estimating  the  size  of  the  tree  is  usually  done  by  one  of  three  plans. 
Some  persons  plot  the  orchard  in  the  day  time,  indicating  the  dose  for 
each  tree,  and  fumigating  at  night  in  accordance  with  this  prearranged 
plan.  They  claim,  with  some  show  of  truth,  that  they  are  better 
acquainted  with  the  trees  by  daylight  and  can  more  accurately  estimate 
their  size.  Others  do  this  at  night,  a  row  at  a  time,  maintaining  that, 
with  practice,  it  can  be  done  with  as  much  accuracy  as  when  done  in  the 
day-time,  and  that  the  danger  of  mistaking  the  rows  is  lessened.  The 
third  plan,  which  seems  the  most  rapid  and  accurate,  is  to  make  the 
estimate  after  the  tent  is  on  the  tree.  The  weighing  of  the  cyanide  is 
done  at  night  as  a  rule,  but  those  working  by  the  third  plan  generally 
have  it  weighed  in  the  day-time. 

When  the  weighing  is  to  be  done  at  night,  a  base  of  supplies  is 
established  as  near  the  center  of  the  field  as  possible,  and  the  cyanide 
and  acid,  as  well  as  the  water,  are  dispensed  at  that  point,  the  gen- 
erators being  carried  there  on  trays.  A  generator  tray  is  a  frame 
holding  four  generators  in  a  row,  or  eight  if  stacked  two  deep;  a 
person  can  carry  two  trays,  or  generators  enough  for  sixteen  tents. 
After  the  chemicals  are  ready,  the  "fumigator"  takes  up  his  tray  of 
cyanide,  and  the  helper  two  trays  of  generators,  and  they  proceed  to 
tent  after  tent,  leaving  and  charging  a  generator  at  each  tent.  When 
half-way  along  the  row,  the  helper  drops  a  tray  that  has  been  emptied; 
when  he  reaches  the  other  end,  both  trays  are  empty.     The  generators 


30 

are  arranged  on  the  trays,  as  are  also  the  doses  of  cyanide  on  the 
fumigator' s  tray,  in  the  order  of  the  trees.  The  next  work  for  the 
fumigator  is  to  estimate  another  row  of  trees,  and  while  he  is  doing 
this  the  helper  gathers  np  the  generators  of  the  previous  row.  They 
soon  both  arrive  at  the  base  of  supplies  and  proceed  to  measure  and 
weigh  the  chemicals  for  a  row  on  the  other  side.  The  details  of  the 
third  method  have  already  been  described. 

When  the  weighing  is  done  in  the  day-time,  the  average  dose  is 
commonly  weighed  into  each  can  or  bag,  and  a  little  added  or  subtracted 
from  the  dose  as  the  size  of  the  tree  may  indicate.  When  the  trees 
are  very  uniform,  the  dose  thus  varying  but  little,  this  may  do  very 
well;  but  if  the  variation  is  greater,  it  will  be  well  to  have  different 
sized  doses  weighed  out.  When  this  is  done  the  can  or  bag  should 
indicate  clearly  the  amount  of  its  contents  by  its  different  shape  or 
character.     This  method  seems  distinctly  preferable  to  night  weighing. 

Charging. — The  generator  now  universally  used  is  the  ordinary 
earthenware  vessel  or  chamber,  the  cheap  yellow  ware  being  generally 
selected.  Some  use  a  perforated  sheet-lead  cover,  but  generally  no 
cover  is  used.  The  fumigator  places  the  generator  on  the  ground 
near  the  trunk  of  the  tree  and  is  then  ready  to  charge  it,  which  he 
accomplishes  by  dropping  the  cyanide  into  the  diluted  acid  in  the  gen- 
erator. He  has  the  cyanide  either  in  tin  cans  or  in  small  paper  bags; 
in  the  former  case  he  pours  the  cyanide  into  the  acid,  keeping  the  can, 
which  he  replaces  in  his  tray,  but  in  the  latter  case  breaks  the  bag 
and  drops  it  into  the  acid,  bag  and  all.  Some  fumi gators  prefer  to 
add  the  acid  last,  in  which  case  the  helper  brings  the  generator  with 
only  water  in  it,  and  keeps  the  acid  in  a  small  pitcher,  one  for  each 
generator.  In  this  case  the  fumigator  puts  the  cyanide  in  the  gener- 
ator, as  before,  and  then  pours  in  the  acid. 

Poisonous  Nature  of  the  Gas. — All  the  work  of  the  fumigator  under 
the  tent  is  done  at  arm's  length.  There  is  no  poison  more  dangerous 
or  fatal  than  hydrocyanic  acid.  The  danger  from  the  gas  is  greatest  as 
it  is  coming  up  from  the  generator.  This  is  so  well  understood  that 
though  the  gas  has  been  used  for  years  by  a  great  many  people,  we 
have  never  heard  of  an  accident  with  it.  There  seems  to  be  no  injur- 
ious effect  from  breathing  the  diluted  gas  that  fills  the  air  when  the 
tents  are  removed,  even  though  it  may  smell  very  strong  and  one  can 
feel  it  very  plainly  in  his  throat  and  chest.  Working  every  night,  for 
months  at  a  time,  does  not  develop  any  abnormal  symptoms,  so  it  can 
be  safely  said  that,  with  proper  care,  there  is  no  particular  danger  in 
the  use  of  the  gas. 

Inspection. — Wherever  fumigation  is  carefully  done  the  tents  will 
be  thoroughly  inspected  every  day.  To  do  this  the  inspector  goes 
beneath  the  tent  as  it  lies  on  the  ground,  and  any  holes  will  be  at  once 
seen  by  the  light  streaming  through;  these  places  are  marked  and 
patches  applied.  Sometimes  the  patch  is  glued  on,  but  the  usual  and 
preferable  way  is  to  sew  it  on.  Sewing  is  done  by  hand  in  the  same 
way  as  sails  are  mended,  or  sometimes  a  sewing  machine  is  used. 


31 
Concluding  Remarks. 


The  uniform  testimony  of  those  that  have  used  fumigation  exten- 
sively is  that  by  no  other  means  at  any  cost  can  as  effective  work  be 
done  as  by  proper  fumigation.  It  is  also  true  that  at  no  place  where 
fumigation  has  been  followed  for  years  is  it  believed  that  the  method 
is  eradicative.  Some,  indeed,  think  that  it  would  be  if  universally  used, 
but  those  longest  acquainted  with  the  process  do  not  claim  that  for 
it.  When  it  is  well  done,  the  insects  that  escape  are  far  below  one  per 
cent;  but  with  insects  capable  of  increasing  several  hundred  per  cent, 
in  a  single  season,  the  destruction  of  over  ninety-nine  per  cent,  is 
certainly  not  a  bad  result. 

The  question  between  fumigation  and  spraying  will  usually  resolve 
itself  into  this :  If  the  interest  of  the  tree  or  crop  demands  a  degree  of 
freedom  from  scale  insects  that  cannot  be  insured  by  one  or  two 
sprayings,  fumigation  will  be  resorted  to.  The  cost  of  cyanide  has 
been  reduced  about  one-half  since  fumigation  was  begun,  and  if  it 
should  be  reduced  to  about  one-half  of  what  it  is  now,  fumigation  would 
probably  entirely  take  the  place  of  spraying  for  scale  insects  on  all 
trees,  as  it  has  now  done  to  such  an  extent  in  the  case  of  citrus  trees 
that  are  so  difficult  to  spray. 

List  of  the  More  Important  Articles  on  Orchard  Fumigation. 

1887 
Morse,  F.  W. :    The  use  of  gases  against  scale  insects.     Bulletin 
71,  University  of  California,  Agricultural  Experiment  Station,  June  12. 

Gives  results  of  experiments  with  hydrocyanic  acid  gas  as  well  as  with  seven 
other  gases.  A  tent  of  oiled  bed-ticking  was  used,  and  the  gases  were  produced  in 
a  sheet  iron  generator  and  blown  into  the  tent  by  means  of  a  pump.  Numerous 
gases  were  used  with  the  hydrocyanic  acid  to  lessen  the  injurious  effects,  the 
most  satisfactory  being  carbonic  acid  gas.  Tables  and  full  directions  are  given 
for  use  on  trees  of  various  sizes. 

Morse,  F.  W. :  The  use  of  hydrocyanic  acid  against  scale  insects. 
Bulletin  73,  University  of  California,  Agricultural  Experiment  Station, 
August  27. 

Contains  a  fuller  description  of  the  apparatus  and  method  generally,  and  the 
results  of  later  experiments  confirmatory  of  those  previously  arrived  at.  Most  of 
the  work  of  these  later  experiments  was  upon  minor  matters  of  detail. 

1888 
Coquillett,  D.  W.:   Report  on  the  gas  treatment  for  scale  insects. 
Report  of  the  United  States  Department  of  Agriculture  for  1887,  pp. 
123-142,  PL  4-6. 

This  article  gives  an  elaborate  account  of  the  methods  of  fumigation,  and  of  the 
experiments  of  the  author  with  a  large  variety  of  gases,  the  most  satisfactory  of 
which  was  hydrocyanic  acid  gas.  He  discusses  the  patent  obtained  by  Hatch  in 
1867,  the  experiments  of  Dimmock  in  1877,  his  own  work  in  1886-87  and  that  of 
Morse  in  the  latter  year.  The  McMullen  tent  is  described,  and  the  Wolfskill, 
Titus,  and  Culver  fumigators  are  described  and  figured.  Full  directions  are  given 
for  the  generation  of  the  gas  by  the  two  methods  devised  by  himself,  and  for  the 
soda  method  originated  by  Morse,  including  tables  giving  amounts  of  chemicals  to 
be  used  on  trees  of  different  sizes.  He  also  discusses  the  methods  of  agitating  the 
air  in  the  tent. 


32 

Coquillett,  D.  W. :  Supplementary  report  on  the  gas  treatment  for 
scale  insects.     Insect  life,  vol  I,  pp.  41-42. 

Gives  the  results  of  analyses  of  certain  brands  of  cyanide,  and  certain  details  in 
the  generation  of  the  gas. 

Klee,  W.  G. :  Report  of  the  State  Inspector  of  Fruit  Pests.  Third 
Biennial  Report  of  the  State  Board  of  Horticulture,  pp.  242-258,  PL 

1-8. 

Makes  extracts  from  Bulletin  73  and  from  United  States  Report  for  1887,  and 
figures  the  Wolfskill,  Titus,  and  Culver  fumigators,  and  the  Morse  generator. 

Morse,  F.  W.:  Experiments  on  the  cause  and  avoidance  of  injury 
to  foliage  in  the  hydrocyanic  gas  treatment  of  trees.  Bulletin  79, 
University  of  California  Experiment  Station,  May  5. 

An  account  of  a  series  of  laboratory  experiments  which  led  the  author  towards 
the  view  that  the  development  of  ammonia  was  the  chief  cause  of  injury  to  foliage. 
He  was  inclined  to  favor  the  second  method  devised  by  Coquillett  as  the  best  for 
producing  the  gas. 

1889 

Coquillett,  D.  W.:  Report  on  various  methods  for  destroying 
scale- insects.  Report  of  the  United  States  Department  of  Agriculture 
for  1888,  pp.  123-133. 

In  the  part  devoted  to  the  hydrocyanic  acid  gas  he  speaks  of  some  minor 
details  in  the  construction  of  the  generator.  The  Leefeld  fumigator  is  described, 
and  a  new  table  given  of  the  amount  of  chemicals  to  use. 

Coquillett,  D.  W. :  Hydrocyanic  acid  treatment  for  scale  insects. 
Insect  Life,  vol.  I,  pp.  286. 

Gives  experiments  with  the  gas  for  red  scale,  its  effectiveness  and  cost.  Also 
the  effects  of  fumigation  on  lady-birds  and  other  insects. 

1890 

Coquillett,  D.  W.:  The  use  of  hydrocyanic  gas  for  the  destruction 
of  the  red  scale.     Insect  Life,  vol.  II,  pp.  202-207. 

Full  details  of  his  experiments  against  the  red  scale,  and  of  the  simplified  gen- 
erator and  new  formula.  A  new  table  of  amounts  used  for  trees  of  different  sizes 
is  given  with  general  directions.     He  prefers  a  black  tent. 

Lelong,  B.  M. :  Improved  fumigating  apparatus.  Report  of  the 
State  Board  of  Horticulture  for  1890,  pp.  469-472. 

Chiefly  abstracts  from  Insect  Life,  vol.  II,  but  contains  working  drawings  of  a 
form  of  the  Preble  apparatus. 

1891 

Craw,  Alexander:  Destructive  insects,  their  natural  enemies,  rem- 
edies and  recommendations,  51  pp.,  Sacramento,  1891. 

On  pages  33-36  the  author  presents  brief  but  comprehensive  directions  for 
fumigating,  and  gives  figures  of  the  Preble  apparatus. 

1894 

Craw,  Alexander:  Gas  treatment  for  destroying  scale  insects  upon 
citrus  trees.  Report  of  the  State  Board  of  Horticulture  for  1893-4, 
pp.  105-109,  PI.  37-38. 

Refers  to  the  poisonous  nature  of  the  gas,  and  gives  directions  for  its  genera- 
tion. Presents  two  tables  of  amounts  to  use  on  trees  of  various  sizes.  And 
describes  and  figures  hoop  and  sheet  tents,  and  gives  formulas  for  treating  the 
cloth  of  the  tents. 


33 

1898 

Johnson,  W.  G. :  Report  of  the  San  Jose  scale  in  Marjdand,  and 
remedies  for  its  suppression  and  control.  Bulletin  57  of  the  Mary- 
land Experiment  Station, 

Pages  72-95  are  devoted  to  hydrocyanic  acid  gas,  treating  upon  the  early 
history,  the  use  in  greenhouses,  and  presenting  an  account  of  the  experiments  in 
Maryland.  Very  complete  directions  and  reports  of  the  experiments  are  given  and 
the  whole  is  well  illustrated. 


RESUME. 
Hydrocyanic  Acid  is  the  most  effective  insecticide  known,    (p.  3.) 

Its  value  was  first  made  known  by  a  publication  from  this   Station. 

(p.  4.) 

Injury  to  foliage  can  be  prevented  in  a  number  of  ways.    (p.  4.) 

Night  work  has  proven  to  be  a  most  important  item.    (p.  6.) 

The  tent  and  other  apparatus  has  gone  through  an  interesting  course  of 
development,    (p.  7.) 

The  dose  of  cyanide   recommended,  has  varied  considerably,  but  the 
original  prescription  is  about  right,    (p.  7.) 

The  tent  as  now  made  is   of  light   duck,  oiled,  sized,  and  painted,  or 
treated  with  cactus  juice  to  make  it  gas  tight,    (p.  11.) 

Bell  tents  operated  in  pairs  by  means  of  derricks  are  much  used  for  the 
largest  trees,    (p.  12.) 

Hoop  tents  are  most  used  and  can  be  moved  from  tree  to  tree  with  great 
facility,    (p.  14.) 

Box  tents  are  a  recent  Eastern  device  having  some  good  points  and  should 
be  tried  here.    (p.  19.) 

Sheet  tents  are  held  in  great  favor  and  may  replace  all  other  kinds, 
(p.  21.) 

Fumigating  according  to  a  well- arranged  plan  makes  the  labor  a  small 
item  in  the  cost.    (p.  24.) 

Accurate  estimation  of  the  area  of  the  tent  is  essential  to   successful 
fumigation,    (p.  27.) 

The  danger  from  poisoning  is  chiefly  when  charging  the  generator,    (p.  30. ) 

The  tents  must  be  inspected  daily  and  kept  gas  tight,    (p.  30.) 

Fumigation  may  finally  entirely  replace  spraying  for  scale  insects,   (p.  31 . ) 


LIST  OF  STATION  PUBLICATIONS  AVAILABLE  FOR  DISTRIBUTION. 


The  edition  of  the  Report  for  1895-97  is  exhausted.  The  supply  of  all  other 
Bulletins  and  Reports  were  destroyed  with  the  Agricultural  Building,  which  was 
burned  in  April,  1897. 


Report  of  Viticultural  Work  of  the  Station;    1887-93. 

Resistant  Vines;   selection,  adaptations,  and  grafting. 

Bulletin  No.  116:   The  California  Vine-Hopper. 

Bulletin  No.  117 :    The  Control  of  Temperature  in  Wine  Fermentation. 

Bulletin  No.  119:   Vine  Pruning. 

Report  on  Grasses  and  Forage   Plants:     Reprint  from  the  Annual 
Report. 

Bulletin  No.  120:   The  Olive  Knot, 

Bulletin  No.  121:   The  Conservation  of  Soil  Moisture,  and  Economy 
in  the  Use  of  Irrigation  Water. 

Circular:   The  Extermination  of  Weeds. 

Seed  Bulletin  for  1898-99:   Distribution  of  seeds  and  plants. 


The  Reports  and  Bulletins  of  the  Station  are  sent  free  to  all  persons  in  the 
State  who  apply  for  them. 


